Strong suggestion (+)
Should
Strong suggestion (-)
Should not / Shouldn’t
Suggestion (option/possibility) (+)
Could
Suggestion (option/possibility) (-)
Could not / Couldn’t
Possibility (+)
Might, Could, May
Possibility (-)
Might not / Mightn’t, Could not / Couldn’t, May not
Intention (wants) / opinion (+)
Would
Intention (wants) / opinion (-)
Would not
Obligation (+)
Must
Obligation (-)
Must not
Necessary (+)
Have to
Necessary (-)
Does not have to / Don’t have to
Polite pemission (+)
May
Polite permission (-)
May not
Permission (+)
Can
Permission (-)
Cannot
Ability (+)
Can
Ability (-)
Cannot
Past ability (+)
Could
Past ability (-)
Could not / Couldn’t